This invention relates to a device for field emission of electrons. More particularly, apparatus and method for manufacture are provided for a field emitter having a mechanically supported extraction gate. Field emission is a well-known effect in which electrons are induced to leave a cathode material by a strong electric field. The electric field is formed by a grid or gate electrode in proximity to a tip or protrusion of the cathode material. A common problem with field emission devices fabricated with grids or gates in close proximity to a tip of cathode material is that an electrical short-circuit may develop along the surface of the insulator layer between the gate and the cathode, which can render the device inoperable. To alleviate the problem, field emission devices have utilized multiple layers of insulator material between the cathode and gate or grid to increase the path length along the surfaces between the gate and cathode. U.S. Pat. No. 6,181,060B1 discloses multiple dielectric layers between the grid and cathode that are selectively etched to form a fin of the less etchable dielectric. The fin increases the path length for electrons along the surfaces between the grid and cathode, thus reducing leakage and increasing the breakdown voltage.
Dielectric layers between the gate and cathode have been undercut to produce field emission cathodes having decreased electrical capacitance. Undercutting refers to the process of removing all or most of the material surrounding a majority of the tips, leaving cavities that encompass multiple tips. A problem with cavities is the deflection of the gate layer above the cavity due to electrostatic or mechanical forces. In order to minimize gate deflection over cavities, U.S. Pat. No. 5,589,728 discloses pillars or post supports spaced throughout the cavities that directly support the gate layer but leave the gate layer unsupported between the pillars or posts. Effective gate support with only pillars and such supports reduces overall emission tip density because the pillars are spaced closely and utilize space where tips could otherwise be located. A lower overall emission tip density can require a larger emission device to produce similar electron emission. Such a device may be too large for utilization in products such as CRTs or electron guns.
Accordingly, a need exists for an improved gated electron emitting device. Such device should provide higher current and current density and have longer lifetime than prior art devices. Preferably, the device should be produced inexpensively utilizing conventional semiconductor fabrication processes.